Experimental and DFT perspectives: Exploring molecular structure, spectroscopic and physicochemical properties of 4-methylimidazolium phthalate monohydrate crystal

A new organic NLO crystal, 4-methylimidazolium phthalate monohydrate (4MIPM), was synthesized and grown by the slow evaporation method. Single-crystal X-ray diffraction analysis verified the formation of the new crystalline material, which was deposited in CCDC number 2417,091. The Rietveld refinement confirms that the Bragg positions are well-fitted with the diffraction peaks, suggesting phase purity and crystallinity. The IR spectrum of 4-methylimidazole, phthalic acid and 4MIPM crystals were recorded. The changes that exist due to interactions have been discussed. The grown crystal was thermally stable up to 100 °C, with decomposition initiating near 200 °C. Optical transmittance studies confirmed that 84 % were in the visible and near-infrared regions. The optimized structure of 4MIPM has been optimized using the DFT/B3LYP method with a 6–311++G(d,p) basis set. The crystal structure of 4MIPM is stabilized by an H-boding network involving the 4-methylimidazolium cation, phthalate anion and water molecules. The global chemical reactivity descriptor properties were studied by HOMO-LUMO analysis. In addition, the structural analysis was done by Mulliken atomic charge, NBO, molecular hyperpolarizability and electrostatic potential analysis. The third-order NLO parameters were evaluated using Z-scan analysis.